This invention relates to internal combustion engines having two inlet valves for each combustion chamber and, more particularly, to a new and improved engine of that type.
Internal combustion engines having two inlet valves are described, for example, in German Offenlegungsschrift No. 2,815,701, wherein a second inlet line is activated for the supply of supplementary air to the combustion chamber only in a high rotational speed range of the engine. Such dual intake valve arrangements provide the fundamental advantage of torque optimization in both low and high ranges of engine speed. As mentioned in that disclosure, this is especially true when the first inlet line, which is open at all speeds, has a smaller flow cross-section than the second inlet line, which provides a supply of air at higher rotational speeds only
An internal combustion engine of similar design is disclosed in German Offenlegungsschrift No. 3,502,699. That engine has two separate inlet lines opening into a common entrance area for two inlet valves and one of the inlet lines is opened by a throttle flap in the higher engine speed range only. That internal combustion engine, in which both inlet lines are supplied with fuel by injection, includes an arrangement for varying the lengths of the two inlet lines as functions of engine speed and for displacing the valve opening curve of the second inlet valve as a function of the speed. By this adaptation of the operation time of the second inlet valve, an optimum utilization of the intake lag effect can be achieved. Such speed-dependent displacement of the valve opening curve, without change in shape and magnitude, with increasing delay for increased speed, however, is complicated and expensive. First, it requires a large engineering outlay to provide the necessary regulation and/or control and, secondly, since the valve opening curve, i.e., the valve stroke as a function of time or crank angle, remains unchanged, it does not produce optimum conditions for filling the combustion chamber in the higher engine speed range.